Adhesion refers to the resistance force required to separate two contact surfaces. The adhesive force corresponding to the resistance force is affected by the properties of the facing surfaces, the chemicals thereof, the micro-environment of the interface, and the like. In particular, wet adhesion refers to adhesion occurring in a wet environment. Synthetic adhesives, which are widely used for the wet adhesion, have the disadvantage that adhesion is weakened by moisture or other contaminants, and adhesion thereof to various surfaces is deteriorated.
As an approach to overcoming this problem, there is a growing interest in bio-inspired adhesives with excellent strength, moisture impermeability and rigidity. Among the bio-inspired adhesives, the area of greatest interest is the use of adhesive proteins secreted by the sea mussels. The mussels secrete adhesive proteins on the surface of natural or artifact structures in the sea, making them strongly adherent thereto in harsh environments. The strong adhesion of these mussels is known to be attributed to the catechol-containing amino acids which is 3,4-dihydroxyphenylalanine referred to as DOPA as found in the adhesive protein structure secreted by the mussel leg tissue.
Currently, the DOPA is known to be an essential component of byssal proteins, which act as cohesive and adhesive. In this technical area, there is a continuing effort to design peptide compounds or polymers with relatively simple structures containing catheter functional groups included in DOAP or DOPA.
As the early examples of the mussel-inspired polymer, DOPA polypeptides were chemically synthesized using solid or liquid peptide substances. Later, polypeptide copolymers of DOPA and lysine were synthesized by ring opening polymerization of NCA monomers. DNA recombination techniques have also been introduced to produce adhesive proteins. Commonly used synthetic methods includes the modification of DOPA, DOPA peptides, or other catechol functional groups to linear or branched polymers using well-known chemical bonding reactions. This approach may be found, for example, in the linear or branched polymers based on polyethylene glycol (PEG) having the DOAP incorporated into the end of the chain thereof. Alternatively, there is a direct synthesis of the bio-adhesive polymer via the polymerization of DOPA or catechol-containing monomers.
Meanwhile, many bio-adhesives have been known to date. However, since such bio-adhesives generally do not exhibit excellent adhesion properties to all materials, appropriate bio-adhesives should be selected depending on the material of the adhesive substrate or the substrate to be adhered or the purpose of the adhesion.